There are various known elements (e.g., casts and internal elements, such as screws, plates, clips, etc.) and methods for permitting the cicatrization of bone parts and/or fragments by holding them together and avoiding their relative movement to the greatest degree possible. For example, an osteosynthesis clip as described in the above mentioned co-pending parent application (hereinafter the “'600 App.”), in addition to clips as described in U.S. Pat. Nos. 5,449,359, 5,660,188, 5,947,999, 5,853,414, and 5,993,476, the entire contents of which are expressly incorporated by reference, refer to elastic clips and methods for osteosynthesis that connect at least two bio-organic tissue members and for aiding osteosynthesis between bone fragments when it is necessary to maintain contact between the severed parts for the duration of the process of re-joinder between them. As described in the '600 App., the clip includes at least two engagement legs extending approximately parallel to one another and including respective distal bridging tips (hereinafter “bridging tips” or “bridging portions”) and respective proximal insertion tips (hereinafter “insertion tips” or “insertion portions”) to be inserted into the bone tissue fragments; and a connecting bridge coupled to the bridging tips of the two engagement legs, the connecting bridge including at least two elongated sections extending along a non-linear trajectory to form a non-linear deformable region, such as a depression or a dome.
As further characterized in the '600 App., bone fragments to be joined are first drilled in locations for later receiving respective engagement legs of the elastic clip. ('600 App., ¶2). Additionally, the clips are capable of receiving soft tissue members, such as muscle, tendons or ligaments, to be joined to the bone members during the osteosynthesis process. (U.S. Pat. No. 5,947,999, FIG. 24-26 (the “'999 patent”)). If necessary, the soft tissue members can be held in place by the clips while also holding bone fragments in place by sliding the soft tissue members between the bridge and bone portions. ('999 patent, col. 7, 1.60 to col. 8, 1.8). Once the insertion tips of the legs are inserted into the bores drilled in the bone fragments to be joined, the elastic clip is grasped by an instrument, and, using a suitable percussion tool, the instrument is struck to push the clip into the bone fragments. ('600 App., ¶2). Once the legs are completely inserted into their respective bores, the elongated bridge sections of the clip are separated by the tool, which causes the legs to approach one another, thereby carrying the bone fragments into frictional contact under pressure. ('600 App., ¶2).
It has been found that, if the elongated bridge sections of the clip are over-separated, for example, by a surgeon applying too much separation force on the elongated bridge sections, then the contact pressure between the bone fragments in an area near the bridge of the clip may exceed the contact pressure between bone fragments in an area near the bone fragments furthest from the bridge. This pressure differential may cause the bone tissue fragments to pivot toward the bridge of the clip, thereby causing a deviation of the longitudinal axis of the bone fragments and the formation of a gap between the fragments, especially nearest the insertion tips of the engagement legs.
A known solution to this shortcoming is a clip having a non-linear deformable region, such as a depression, provided along the elongated sections of the clip. ('600 App., FIGS. 1, 2, 3a-3d). After the clip is inserted into drilled holes in each bone fragment on either side of the fracture, a first force is applied on the elongated bridge sections to separate the opposed elongated sections of the bridge section. This causes the engagement legs to move toward each another. However, the legs may pivot in such a way that a gap may be formed at the portion of the fracture opposite the clip. ('600 App., FIG. 3c). A second force, such as an upward force, is applied in the non-linear deformable region of the bridge sections thereby causing a partial linearization of the non-linear deformable region. This second force causes the inserting portions to pivot toward one another about the bridging portions, thereby causing any gap to close between the bottom surfaces of bone tissue fragments. ('600 App., FIG. 3d). While applying the second force to the elongated sections, withdrawal of the clip from the bone fragments may be prevented by simultaneously applying a third force opposite to the second force, such as a downward force, on the bridge section near the bridging portions of the engagement legs. However, in the case of a stepped clip, as illustrated in FIGS. 4a and 4b of the '600 App., for joining bones of different diameter, it has been found that the known insertion tool, as claimed in the '600 App., and the patents referenced therein, requires improvement for better engaging the bridging tips of the engagement legs in order to apply the third force. Also, the tool must be configurable to be reusable on either a non-stepped or a stepped clip. As will be shown herein, the tool is incapable of engaging the stepped clip in a stepped down region in order to apply the third force at that region and thereby can not effectively counter the second force applied to the non-linear deformable region. The present invention addresses this issue.
It has further been found that the known removal procedures of a clip from the bone fragments can cause excessive damage to the bone fragments. One manner in which the bone fragments are damaged is by the traction forces created when clips having spikes or retaining teeth for gripping the bone are removed from bone fragments with a direct sheer force formed by pulling the clip transversely from the bone with forceps. Also, such a direct linear removal of the clip often requires insertion of a lever between the clip's bridge and the bone surface to pry the clip from the bone. The traction forces associated with such removal procedures causes the retaining teeth to tear the original bony channel as they exit the bone, causing trauma. Moreover, such traction forces can further damage the bone by causing splints or fractures and can further thwart the intended healing process by causing undesired displacement of the bone fragments. To the extent that clips have employed screw-like threads to advantageously facilitate the removal of the clip after the bone tissue has been fused (See '600 App., FIG. 8a-8c), this also has shortcoming to which this invention is directed. Removal is obtained by cutting away the bridge at the locations of bridging tips 140a and 140b to remove the bridge, as shown in FIG. 8b of the '600 App. Once the bridge is removed, the engagement legs may be removed from the bone tissue, for example, by separately unscrewing each engagement legs in a counterclockwise direction, as shown in FIG. 8c of the '600 App. However, the known clips, as presented in the '600 App., have only partially threaded legs—either provided near the insertion tips or, alternatively, near the bridging tips. Therefore, upon removal, the threaded region cuts through the boney channel of the area of the bone corresponding to areas of the engagement members that were not threaded. (See '600 App., FIGS. 8a-8c). The present invention addresses this issue by redesigning the engagement legs with more effective threading.
Additionally, with the advancement of thorascopic surgical techniques requiring the insertion of tools through small tubes and openings to perform ever more delicate surgeries, i.e. spinal surgery, it is also advantageous to limit the number of tools that are used and the amount of manipulation required to position the clip. Therefore, the use of thermally sensitive materials or shape memory alloys for creating the necessary deformation of the bridge member as opposed to physical manipulation by tools is advantageous. As such, the present invention solves these problems associated with the known tools and the required physical manipulation of the clip by incorporating shape memory alloys into the improved clip. In and of themselves, shape memory alloys such as Nitinol have been well known. See for example, U.S. Pat. No. 3,174,851. Other metals, such as AuCd, FePt.sub.3, beta Brass and InTI, also exhibit shape memory behavior. These materials have the property of changing shape in response to a change in material temperature. This shape change potential is imparted into the memory metal device through a series of heat treatments. The transition temperature range is imparted to the material through varying mixtures of intermetallic compounds such as nickel-titanium and heat treatment. The heat treatment methods for the material generally consist of at a minimum high temperature setting of the desired final shape of a device followed by a low temperature straining of the device to a second shape. Then, when the device is in the second shape and brought to the transition temperature the device returns to the preprogrammed final shape. The shape change occurs due to the transition of the material from a martensitic to austenitic phase microstructure. These heat-initiated changes cause gross changes in the shape of the implant formed from memory metal. Further detail regarding the creation and properties of shape memory alloys can be found in U.S. Patent Application Publications 2002/0029044 to Monassevitch, 2004/0172107 to Fox and 2002/0173793 to Allen, all of which are fully incorporated by reference.